As described, for example, in JP10-085536A and JP2001-143524A, ventilation members used for automobile components (lamps, motors, sensors, switches, ECUs, and so forth) make use of a gas permeable filter (gas permeable membrane) having gas permeability, dustproofness, and waterproofness. Adaptation of such ventilation members to electrical devices, such as mobile communication devices, cameras, electric shavers, and electric toothbrushes, now is being discussed.
The ventilation members as described above play a role of eliminating a pressure difference between the interior and the exterior of the device, propagating sounds, or discharging a gas generated inside the device while preventing the entry of dust or water into the interior of the device. For instance, fogging possibly occurs on a headlight of an automobile with a change in temperature, and ventilation members are adopted with the aim of preventing or eliminating the occurrence of such fogging.
Incidentally, if we assume that the dustproof and waterproof capabilities are the same, then ventilation members are more efficient if they require a shorter time to eliminate a pressure difference between the interior and the exterior of the device or a shorter time to discharge a gas generated inside the device. These times can be shortened by increasing a gas permeation quantity per unit time of the ventilation members.
Increasing a gas permeation quantity of the ventilation members, however, is not readily achieved. The bottleneck in a gas permeation quantity is a gas permeable filter that has large gas permeation resistance, but the gas permeable filter has been improved to the point that further improvement is difficult.
As the ventilation members per se increase in size, the gas permeation quantity naturally increases in proportion. Size changing of the ventilation members, however, is not readily adopted, because it involves a design change at the other end (at the device end).
Further, in recent years, there has been a need for ventilation members that excel more in durability against foreign matter, such as water droplets and dust. For example, as ventilation members to be used for lamps or the housings of ECUs in an automobile, there is a need for ventilation members not only capable of withstanding car washing, in particular, high-pressure car washing, but also capable of completely preventing the entry of water into the interior of the housings.